A ground source heat pump is one that uses a below ground coil, (referred to herein as the outdoor coil), with refrigerant therein, to transfer heat to or from the ground. The coil acts as an evaporator and condenser in the overall system design dependent upon the mode of operation, i.e. heating or cooling. The natural heat from the ground can then be used to either heat or cool an enclosed space such as a residence, commercial building or the like. The native earth is a heat source in the heating mode and a heat sink in the cooling mode. The heat pump also has an indoor unit that is connected to the outdoor coil and controls the heating and cooling operations.
There have been attempts over the years to perfect this technology by addressing some faults to the system that affect performance. One problem with existing systems is known as "hunting" which makes it impossible to maintain a constant and consistently high coefficient of performance (COP) level. "Hunting" is an uncontrolled underfeed/overfeed by the thermostatic expansion valve (TXV) (metering device) of the system that results in very wide and severe pressure fluctuations on the heating mode where the ground collector coil is an evaporator. With wide evaporator fluctuations it is impossible to maintain constant the Coefficient of Performance (COP) and drastically reduces the heat the heat pump can produce in the heating mode.
In the cooling mode, after a heating season is over and the heat pump is switched to the cooling mode, the ground collecting coil becomes a condenser rejecting heat from the heat pump. Because the ground is frozen the refrigerant liquifies in the ground coil at to low a pressure and temperature, e.g. 20.degree. F. & 50 to 60 PSIG. This causes a lack of flow or severely reduced flow back out of the ground coil to supply the thermal expansion (TX) valve with the proper amount and pressure of refrigerant. This lack of flow will prevent the heat pump from operating properly in the cooling mode. To counteract this problem most heat pump systems have twice as much refrigerant charge for the cooling mode as for the heating mode. This method has offered a very limited success but increases the refrigerant charge.
A large quantity of refrigerant, in the event of a leak, is dangerous because a popular refrigerant R-22 is heavier than air and displaces air. This could cause suffocation of occupants of the space subject to air conditioning. Limited control of the refrigerant gases in most systems on the market, especially in the cooling mode that requires double the refrigerant charge, poses threats to the environment and people should there be a leak. Some known designs require 80 pounds or more gas refrigerant.
Improperly designed outside copper coils in both the design of and size of and, in vertical installations particularly, the length of has been a source of problems with existing systems. Undersized ground coils have been used to minimize the refrigerant charge.
Excessive refrigerant levels for many reasons that are due to poor design of the refrigerant controls in the system, and poorly designed ground coils have also been a problem associated with existing systems.
Inadequate return of the refrigerant gases and refrigerant oil to the system is another problem of existing systems which causes poor COP's, and erratic behaviour in system performance as well as early equipment failure, particularly failure of the compressor.
U.S. Pat. No. 5,136,855 issued Aug. 11, 1992 concerns a ground source heat pump. In the patented system there is an accumulator with refrigerant level sensor. The system includes an indoor coil circuit with an indoor coil and an outdoor coil circuit with an outdoor coil and a scroll compressor. The accumulator is used for separating gaseous refrigerant from liquid refrigerant. A level switch, which when the heat pump is in the cooling mode, controls a solenoid valve connected in parallel to a thermal expansion valve to change a base refrigerant flow to the indoor coil when the refrigerant level in the accumulator drops below or rises above a preset level. The control means is intended to increase efficiency but even with that it is believed the system in the heating mode has a COP of about 2.5. In the heating mode most systems operate at a COP of about 4 or slightly above. U.S. Pat. No. 5,038,580 issued Aug. 13, 1991 to David P. Hart is also directed to a ground source heat pump system. The patentee indicates that a coefficient of performance (COP) of 3 is easily obtained for a heat pump using a direct earth coupled underground heat exchanger. The patentee indicates at column 2, lines 43 to 45 that "Approximately twice the quantity of refrigerant charge is required in the cooling cycle as compared to the heating cycle". The unit is sized to meet cooling requirements but in order to operate properly during the heating season a portion of the refrigerant charge is stored. The exchanger tubes in the earth vary in diameter from one end to the other with the smaller diameter being at the bottom and the larger diameter at the top. In the cooling mode, as the refrigerant expands from liquid to vapour in flowing upwardly the exchanger tube diameter increases to maintain appropriate velocities for optimum pressure drop.
An object of the present invention is to provide a heat pump which is safe to both the consumer and the environment by reducing the amount of refrigerant from that conventionally used in known systems. The aim is to reduce the refrigerant levels to about half of what most existing systems use particularly in the cooling mode.
A further principal object of the present invention is to provide a ground source heat pump in which approximately the same quantity of refrigerant gas is used in each of the cooling and heating modes.
A further principal object of the present invention is to provide a ground source heat pump system that has a coefficient of performance of approximately four in the heating mode and in the cooling mode, an energy efficiency rating (EER) of about 12.
A further principal object of the present invention is to minimize or reduce the "hunting" as this has a negative effect on the COP.
A further principal object of the present invention is to provide a ground source heat pump system in which the refrigerant gases are under control to thereby render predictable performance.
A further principal object of the present invention is to provide an improved piping system for the ground coil.
A further principal object of the present invention is to provide a piping system for the ground coils in which portions are blocked off until predetermined, preselected conditions are met.